Pipe systems often include complex arrays of closely spaced pipes which circuitously pass through manufacturing, refining or research facility. The pipes often are very close to one another along at least portions of their respective lengths. Valves are disposed at selected locations along the pipes to control the flow of fluid. Each valve includes a housing having opposed longitudinal ends and a flow passage extending therebetween. The ends of the valve housing are connectable respectively to axially aligned pipes. A valving member is mounted in the housing between the opposed ends for selectively blocking the flow of fluid through the housing.
Butterfly valves and ball valves are widely used in industry. The valving member of a butterfly valve is a generally planar disc rotatably mounted in the housing. In one rotational orientation the plane of the disc is aligned along the axis of the flow passage in the valve housing to enable fluid to flow on either side of the disc. In another rotational orientation the plane of the disc is orthogonal to the axis of the flow passage to completely block the flow of fluid through the valve housing. The valving member of a ball valve is a ball rotatably mounted in the valve housing. A flow passage extends diametrically through the ball and defines a cross-section substantially the same as the flow passage through the valve housing. In a first rotational orientation of the ball, the flow passage through the ball is coaxial with the flow passage in the valve housing to permit a flow of fluid through the housing. In a second rotational orientation the flow passage through the ball is orthogonal to the flow passage through the valve housing. Thus, a continuous spherical surface on the ball blocks the flow of fluid through the valve.
The disc in the prior butterfly valve and the ball in the prior art ball valve each are rigidly mounted to a valve stem which extends through the valve housing substantially orthogonal to the axis of the flow passage. A rotation of the valve stem causes a corresponding rotation of the disc or ball for selectively opening or closing the flow passage through the housing of the prior art valve. The valve stem and the valve housing of the prior art butterfly valve and the prior art ball valve generally are constructed with stops to enable only 90.degree. of rotation of the valve stem. Thus, a valve being moved from the open position toward the closed position will be prevented from being rotated beyond the closed position back into a fully opened position. Similarly, a valve being rotated from the closed position toward the open position will be prevented from rotating beyond the partly open position into a partly closed position. However, the valve stem can be stopped at any point within this 90.degree. range of motion to achieve a partly opened or partly closed condition.
Complex systems of pipes generally require precise on-off sequencing of valves. To achieve precise control, the prior art pipe systems include actuators that are operatively connected to the respective valves. For example, the prior art valve housing may include a bracket in proximity to the valve stem. The prior art actuator may be mounted to the bracket of the prior art valve housing, and includes a shaft that can be operatively connected to the valve stem. The typical prior art actuator is pneumatically operated to rotate the actuator shaft and the valve stem through the 90.degree. permitted by the stops on the prior art valve stem or valve housing. A substantial number of actuators employed in a complex prior art pipe system may be simultaneously operated such that a first plurality of valves in the system are simultaneously opened while a second plurality of valves in the system are simultaneously closed. An extremely effective prior art actuator is shown in U.S. Pat. No. 4,556,194 which issued to van Lingen on Dec. 3, 1985 and which is assigned to the assignee of the subject invention. The disclosure of U.S. Pat. No. 4,556,194 is incorporated herein by reference.
System operational considerations may require certain valves within a complex pipe system to be only partly opened or partly closed. For example, it may be desirable to have a valve slightly opened to prevent an excessive build-up of pressure within a system. Alternatively, it may be desireable to have a valve slightly less than fully open to reduce the maximum flow rate of fluid through the valve. In still other situations it may be desireable to more significantly affect the flow of fluid through the valve. For example, it may be necessary or desireable to have a valve operate only between a substantially fully closed position and a half-opened position. Specially manufactured valve housings or valve actuators can be provided for these purposes. However, the specialty valves and actuators are extremely expensive. Furthermore, the exact degree of opening or closing often may not be known until the system is tested or calibrated, and it may be desireable to change certain valve operational limits from time to time. It also is more desireable and more cost efficient to use off-the-shelf components.
The prior art has included travel stops that can be retrofitted to the portion of a valve actuator facing away from the valve housing. In particular, a prior art actuator can be partly disassembled in the field, and a cam can be mounted to the actuator shaft to extend beyond the portion of the actuator facing away from the valve housing. The prior art actuator cam is provided with first and second cam faces extending radially outwardly and separated from one another by 90.degree.. This prior art actuator is further retrofitted with a pair angle brackets having a pair of parallel bolts threadely engaged therein. The parallel bolts extend orthogonal to the direction of fluid flow through the valve and on the portion of the actuator facing away from the valve. The parallel bolts are disposed to engage the respective first and second cam faces of the cam retrofitted to the actuator shaft as the respective cam faces are rotated toward an alignment parallel to the direction of flow through the valve. Advancement of either of the parallel bolts can prevent the corresponding cam face of the retrofitted cam from reaching an alignment where it is perfectly parallel to the direction of fluid flow through the prior art valve. In this manner, the parallel bolts retrofitted to this prior art actuator can prevent the actuator from completely closing the associated valve or from completely opening the associated valve.
This prior art travel stop has several deficiencies. First, the alignment of the bolts parallel to one another and orthogonal to the direction of flow substantially limits the range of adjustments. In particular, one or both cam faces will have to undergo substantial rotation before contacting even a fully advanced bolt. Thus, for example, this prior art actuator and stop assembly may not be helpful if it is desired to ensure that the valve rotates only from a fully closed position to a slightly opened position. Second, the parallel alignment of the adjustable bolts in the prior art apparatus is such that the bolts will be contacted from the side when the bolts are rotated into more fully advanced positions. Consequently, substantial bending moments will be exerted on each bolt during each actuation of the valve. The bending moments can cause deformation and breakage of the bolts with substantial down time for an entire chemical or petrochemical processing system. Thus, these prior art travel stop devices are not well suited for systems where a full range of control of the valve is desired.
In addition to these operational limitations, the disposition of the prior art travels stop on the side of the actuator opposite the valve can create problems. First, the location of the prior art travel stop can create significant torsional forces on the actuator shaft. In this regard, one end of the elongated actuator shaft will exert forces on the valve stem, while the other end of the elongated actuator shaft will have forces exerted on it by the prior art travel stop mechanism. Additionally, the disposition of the prior art stop mechanism on the side of the actuator opposite the valve adds to the total space required for the prior art valve and actuator assembly. As noted above, pipes often are very close in many industrial facilities and significant expansion of the space envelope required for the prior art travel stop assembly may not be possible. Furthermore, many pipe systems are employed in environments where an accumulation of dirt or debris is possible. A stop mechanism disposed on a portion of the actuator facing away from the valve is exposed and hence susceptible to an accumulation of debris that could alter the performance of this prior art travel stop assembly.
In view of the above, it is an object of the subject invention to provide a travel stop assembly for adjusting the rotation of a valve through a full range of rotational orientations between a fully closed position and a fully opened position.
It is another object of the subject invention to provide a travel stop assembly that can be employed with available valves and available actuators.
An additional object of the subject invention is to provide a travel stop assembly disposed to avoid interference with adjacent valves, pipes or fittings.
A further object of the subject invention is to provide a travel stop assembly that is substantially protected from an accumulation of dirt or debris that could affect the operation of the valve and the actuator.
Yet another object of the subject invention is to provide a travel stop assembly for an actuated valve where the adjustable components are not subjected to excessive bending moments at either end of their range of adjustments.